Marker interface for listeners that expect to receive plugin system-related events (e.g.
PluginFrameworkStartedEvent). This interface is used to enforce a happens-before
relationship between construction of the listeners and constructions of JIRA's plugin manager. If the listener does
not implement this interface, there is currently no way in JIRA to inform PICO that the listeners need to be
instantiated before the plugin manager does its thing.
Not implementing this interface may mean that your listener will miss events.